In the well-known process of electrophotographic or xerographic printing, an electrostatic latent image is formed on a charge-retentive imaging surface, typically a “photoreceptor,” and then developed with an application of toner particles. The toner particles adhere electrostatically to the suitably-charged portions of the photoreceptor. The toner particles are then transferred, by the application of electric charge, to a print sheet, forming the desired image on the print sheet. An electric charge can also be used to separate or “detack” the print sheet from the photoreceptor.
For the initial charging, transfer, or detack of an imaging surface, the most typical device for applying a predetermined charge to the imaging surface is a “corotron,” of which there are any number of variants, such as the scorotron or dicorotron. Common to most types of corotron is a bare conductor, in proximity to the imaging surface, which is electrically biased and thereby supplies ions for charging the imaging surface. The conductor typically comprises one or more corona members, such as wires (often called a “corona wire”) or a metal bar forming saw-teeth (a “pin array”), the conductor extending parallel to the imaging surface and along a direction perpendicular to a direction of motion of the imaging surface. Other structures, such as a screen, conductive shield and/or nonconductive housing, are typically present in a charging device, and some of these may be electrically biased as well. A corotron having a screen or grid disposed between the conductor and the photoreceptor is typically known as a “scorotron”.
In one type of charging device of particular interest with respect to the present invention, a charging electrode may be provided in the form of an electrically conductive strip having projections, scalloped portions, or teeth members integrally formed with, and extending from, a longitudinal edge of the electrode. This arrangement, known as a pin array electrode, provides significant structural and operational advantages over other types of electrode devices such as thin wire electrodes, including comparatively high structural strength, greater charge uniformity and reduced levels of undesirable ozone emissions. In this respect, U.S. Pat. No. 3,691,373 to Compton et al. demonstrates a corona generating device generally comprising a pin array electrode supported on either side by support strips, and mounted within an electrically nonconductive base member. One of the side strips is adapted for connection to an exterior connector from a high voltage source. The electrode is fixed into position within the base member by a plurality of transverse pins which fit through matching holes in the base member, the pin array, and the support strips. The corona generating device disclosed therein may further include a screen and/or an auxiliary electrode as well as various additional conductive shields for regulating charging current to control uniformity of charge. A detailed description and illustration of pin array corona generating devices, specifically describing the mounting mechanism used to support a pin array electrode in a corotron device is provided in U.S. Pat. Nos. 4,725,732 and 4,792,680, the entire contents of which are hereby incorporated by reference herein.
Several problems have historically been associated with the unique design of pin array corona generating devices. Generally, it is important that the pin array electrode, which is typically stretched between mountings at opposite ends of the corona generating device, is maintained under tension so as to be in a taut condition. Any looseness and/or kinks in the electrode member may result in a non-uniform charge derived from the corona generating device. In order to insure that the electrode member is sufficiently supported, the pin array electrode is conventionally mounted between support members, as shown in previously referenced U.S. Pat. Nos. 4,725,732 and 4,792,680.
It is also desirable, in corona generating devices, to provide an arrangement for easily replacing faulty or a deteriorated corona generating electrode upon failure, or preferably, for replacing a corona generating electrode prior to failure through preventative maintenance. Typically, the replacement of a pin array electrode necessitates replacement of the entire assembly of the corona generating device, creating waste and additional expense. Since replacement is usually handled by a service technician at the commercial site at which the machine is located, ease of replacement and adjustment in a minimum amount of time is essential. Thus, it is an object of the present invention to provide a pin array corona generating device that is cost effective and serviceable while eliminating waste by permitting the replacement and adjustment of the corona generating electrode within a corona generating device.